1. Field of the Invention
This invention relates to semipermeable membranes useful in reverse osmosis and a process of making them.
2. Description of the Prior Art
Reverse osmosis has been an object of intense study for the purposes of separating water from an aqueous solution of organic or inorganic solutes, and particularly, for the desalination of sea water. The principle of reverse osmosis is well known. The most critical factor in this technique is in the use of a semipermeable membrane having adequate physical and mechanical properties. The membranes should be keenly selective relative to the species to be transported even with very small pressure differences. They must have sufficient mechanical strengths to withstand against the pressure difference in the operating conditions and also high durability for a long period of continuous service.
As the semipermeable membranes useful in the reverse osmosis, there have been proposed those prepared from cellulose derivatives, such as, cellulose acetate, and polyamide or nylon. Among them, products from cellulose acetate have been considered superior. However, the cellulose acetate membranes are still not perfect and have the following defects:
1. they are sensitive to chemical attacks by alkalis or acids leading to a deterioration in their properties; PA1 2. consequently, the pH range of the treating solutions usable in the process is limited; PA1 3. they have low resistance against organic solvents and poor durability and are not adaptable to a wide temperature range.